The skeletal effects of sex steroids can be dramatic; bone loss is rapid in oophorectomized women, and serum estrogens appear to be the strongest determinants of bone loss in the immediate perimenopausal period. The studies proposed here address the contributions of sex steroid concentrations to: 1) bone loss in premenstrual women; 2) bone loss in women at least 5 years postmenopausal; 3) bone loss in older man; 4) the association between genetic influences on bone mass in young women; and 5) the black/white differences in bone mass in young women. These studies are proposed to expand upon the work done in our current grant focused on sex steroids and changes in bone mass around the time of the menopause. We hav found that serum estrogens are the strongest predictors of bone loss in thi period and that testosterone concentrations are weaker but independent predictors of bone loss in these same women. However, by five years past the menopause, estrogen levels have declined to such a level that we were unable to detect estrogen effects on bone loss, although the influence of testosterone remained. We are now proposing a test of the hypotheses that androgen concentrations are linearly associated with rates of bone loss in older men and women. In younger women, we have found both estrogen and androgen associations with bone loss, and androgen associations with bone mass. This has led to the hypotheses that: 1) androgen concentrations are associated with bone mass in younger women; 2) familial similarities in estrogen and androgen concentrations account for a portion of the observed heritabilities in bone mass; and 3) at least a portion of the well established black-white differences in bone mass is related to black-white differences in sex steroid concentrations.